1. Field of the Invention
The present invention relates to an area sensor (semiconductor device) having an image sensor function and a display function. In particular, the present invention relates to an area sensor (semiconductor device) that has EL (electroluminescence) elements as a light source and is composed of photoelectric conversion devices provided on a flat surface (insulating surface) and a plurality of thin film transistors (TFTs) arranged in a matrix.
2. Description of the Related Art
In recent years, a solid-state image sensing device is being used, which has diodes, CCDs, or the like for reading an electric signal having image information from a light signal having textural/graphic information, video information, and the like on a sheet of paper. Such a solid-state image sensing device is used for a scanner, a digital camera, and the like.
The solid-state image sensing device having photoelectric conversion devices are classified into a line sensor and an area sensor. In the line sensor, photoelectric conversion devices provided in a line shape are scanned with respect to a subject, whereby image information is captured as an electric signal.
The area sensor is also called a contact-type area sensor, in which photoelectric conversion devices provided on a flat surface are disposed on a subject, and image information is captured as an electric signal. Unlike the line sensor, it is not required to scan photoelectric conversion devices in the area sensor, so that a motor and the like for scanning are not necessary.
FIGS. 23A and 23B show a configuration of a conventional area sensor. FIG. 23A is a perspective view of the area sensor, and FIG. 23B is a cross-sectional view thereof. A sensor substrate 2501 with photoelectric conversion devices formed thereon, a backlight 2502, and a light scattering plate 2503 are provided as shown in FIG. 23B.
Light from the backlight 2502 (light source) is refracted in the light scattering plate 2503, and is radiated to a subject 2504. The radiated light is reflected from the subject 2504, and radiated to the photoelectric conversion devices provided on the sensor substrate 2501. When the photoelectric conversion devices are irradiated with light, a current with a magnitude in accordance with the brightness of light is generated in the photoelectric conversion devices, and image information of the subject 2504 is captured in the area sensor as an electric signal.
In the above-mentioned area sensor, when light is not radiated uniformly to the subject from the backlight 2502, a read image may partially become light or dark, resulting in inconsistencies of the image. This makes it necessary to design the light scattering plate 2503 so that light is radiated uniformly to the subject 2504, and to precisely adjust the position of the backlight 2502, the light scattering plate 2503, the sensor substrate 2501, and the subject 2504.
It is also difficult to minimize the size of the backlight 2502 and the light scattering plate 2503, which prevents the area sensor from becoming small, thin, and light-weight.